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Strength of Chain and Ropes.                  397

The   Strength of Chain.—Both sides of the link resist
tension, so taking f = 4 tons safe :

but    r = -    .'. W = 6-28

2          --------------

4 x 4 = 25*12 rz
1 tons safe load.

Sir Jno. Anderson deduces a simple rule from the above :
(dia. in eighths)2
10

"Safe load in tons.

Thus an inch chain bears------= 6*4 tons.

,                                   i o               _

Strength of Ropes.—For white hemp ft — \ ton safe. But
as all ropes are measured by their circumference, and area = —~

Strength of hemp rope = £ x ~~ == "°4 circ'2 (tons)-

Wire rope has its members stated by their W.G. Referring to
page 276, the total area may be reckoned: then let/t= n| tons
safe for ir6n or steel.

Strength of Pipes and Cylinders, pressed internally.
Imagine a hemispherical vessel A, Fig. 351, hung by a string, and

pressed internally; then, as the vessel moves neither to right or
left, it follows that the total pressure on the curved surface in
direction F is equal to that upon the flat surface. The flat surface
is called the * projected area' of the curved surface.